Estimation of Hypochlorites in Commercial Bleaching Solutions by Cl- ISE and Platinum Electrode

 

Ismail K. AL-Hitti, Ahmed SalihLateef

Department of Medical Laboratory Techniques, AL-Ma'arif University College, Anbar, Ramadi, Iraq.

*Corresponding Author E-mail:

 

ABSTRACT:

Chloride ion – selective and platinum electrodes were successfully applied in the determination of hypochlorites in commercial bleaching solutions. The results obtained with Cl- ISE are compared to those obtained with Pt electrodes since the reactions are oxidation –reductions where the Pt responds to their potential change. A clear change and jump at equivalence points were found and titration curves are in S form which were approved by first and second derivatives. The percentages obtained with Cl- ISE are relatively larger than results with Pt electrode which are due to practical errors, interference of I- ions and little Cl- by –Product of hypochlorite manufacture. In general, almost both electrodes offered results in the range of 3-8% solutions of hypochlorites within the period of storage. Low results may by due to wasting and decomposition by temp, transferring, dilution and stirring the solution.

 

KEYWORDS: Cl- ISE, Hypochlorite, Bleaching solutions, Potentiometric titration, Iodimetric technique.

 

 

INTRODUCTION:

Hpochlorus acid (HOCl) is produced when Cl2 gas is treated with water which occurs according to the aquation:-

Cl2 + 2H2O Cl-                           H3O+ + HOCl(1).

 

The acid HOCl is weak with a dissociation constant of 3.2 x 10 -8 and exists only in aqueous solutions. HOCl is a powerful oxidizing agent, stronger than MnO4–(1). Sodium hypochlorite can be made by neutralization of HOCl solution, but it is produced more economically by the disproportiona of chlorine in basic solution.

 

Cl2+ 2OH-                                   Cl-  + ClO-  + H2O

 

Solution of hypochlorite ion so produced are sold as laundry bleaches, e.g chlorox. Sodium hypochlorite is used as a bleaching material and well- known reagent in volumetric analysis(2).

 

Another type of common bleach is called bleaching powder or chlorinated lime written as:                                                                   

CaOCl2 or Ca(OCl)2and prepared by treating calcium hydroxide with chlorine :

2Cl2+2Ca(OH)2Ca(OCl)2                          CaCl2 + 2H2O

 

Hypochlorite is anti bacterial agent (is used foranti microbial washing solution). It is commonly known as bleach or liquid bleach which is frequently used as a disinfectant or bleaching agent(3). A 12% solution is widely used in water works for chlorination of waters (4). and a 15 % solution is more commonly used for disinfection of waste water in treatment plants (5) and as an irrigant during dental procedure as well as antisepting agent (6, 7).

 

Dilute solutions of hypochlorite (50ppm to 1.5 %are found in disinfection sprays and wipes used on hard surfaces (8).

 

Chloro-oxygenated agents compounds (including sodium hypochlorite) were determined individually and in mixtures by potentiometric titrations with Cl- ISE and Pt electrode. Good and encouraging results were obtained with concentrated as well as with diluted solutions of these agents (9).

 

Transport and handling safety concerns have directed public opinion towards the use of sodium hypochlorite rather than chlorine gas in water treatment which represents a significant market expansion potential (10).

 

Sodium hypochlorite has distaining properties, it can be used to remove mold stains, dental stains caused by fluorosis, and stains on crockery, in particular those caused by the tannins in tea (11). In batch treatment operations, NaOCl has been used to treat more concentrated cyanide wastes such as silver cyanide plating solutions. Toxic cyanide is oxidized to cyanate (OCN-) that is not toxic(12).

 

CN-+ OCl-                                      OCN- + Cl-

 

Sodium Hypochlorite is used in endodontics(13, 14), and in nerve agent neutralization(15, 12). Looking through this review, it is clear that hypochlorite has multi uses and it is widely spread in markets in containers for washing, bleaching and disinfection(Table1).

 

Table (1) : Some Physical and Chemical Properties of two types of hypochlorite.

Component

Potential(V)

Density g/cm3

Melting point oC

Boiling pointoC

Solubility in water g/100ml(25oC)

NaOCl

0.9

1.11

18

101

29.3

Ca(OCl)2

0.89

2.35

175

Not applicable N/A

21

 

 

These applications require knowledge of exact concentrations of these containers in order to insure their suitable uses. Thus, the aim of this research is to study the specifications of different types of hypochlorites and find out their concentrations using chloride and platinum electrodes in potentiometric titrations in anacidic media.

 

EXPERIMENTAL PART:

Materials:

All chemicals used in this research were highly graded or ANALAR and used without pretreatment. All solutions were prepared in twice distilled water at 25 Co. Potential difference measurements were done by Ion analyzer, Digital from Mettler – Toledo (China)/.Cl- ISE and Pt electrodes were from Mettler-Toledo (China) and used for following potential changes with accuracy of±0.01 mV unit.

 

Combined glass electrode from Mettler – Toledo (China) used for following pH change with an accuracy of±0.01 pH unit. Double junction calomel electrode also from Mettler – Toledo (China) was used as reference electrode. Its an external barrier was filled with saturated KNO3 solution to avoid Cl- interference from internal barrier.

 

Standardization of KI solution (16):-

10 ml of KI solution were transferred into conical flask and titrated with an excess of 0.1 N AgNO3 solution from burette, 3-4 drops of Fe+3solution were added in addition to 6 M HNO3 , and back titrated with 0.1 N SCN- solution till the appearance of red solution colour. The titration was repeated three times and the mean value of KI solution concentration was found = 0.0833N.

 

Starch solution:

1.0 g of soluble starch was treated with small volume of water to prepare its paste which mixed well and poured in 100 ml of boiled distilled water, boiled for 1 min and left to cool and kept in firmly closed bottle.

 

Standardization of Na2S2O3.5H2Osolution:

10 ml of 0.1 N KIO3 solution were transferred into conical flask and 10 ml of 10 % KI solution was added with 30 ml of 2M H2SO4. The liberated I2 was titrated with prepared Na2S2O3 solution until the appearance of light yellow, 1-2 ml of starch solution added. Titration was resumed until colourless. The titration was repeated three times and the concentration was found = 0.1 N.

 

Standardization of I2 solution with standardized solution of Na2S2O3.5H2O:

10 ml of I2 solution were transferred into conical flask and titrated with Na2S2O3.5H2O solution until the solution faded, 1 ml of starch solution was added and titration was resumed until colourless. The titration was repeated three times and concentration of I2solution was calculated to be 0.094 N.

 

Standardizations of Sodium and Calcium hypochlorites :

Approximately 0.1 N of each salt solution were prepared in twice distilled water and diluted with 30 ml of distilled water and 30 ml of 1M H2SO4and excess of Standardized I2 solution. The excess of I2 solution was titrated with standardized Na2S2O3 solution until the appearance of light yellow colour. 1ml of starch solution was added and the titration was resumed until colourless. The concentrations were found to be 0.0292 N NaOCland0.1048N Ca(OCl)2.

 

Determination of Sodium hypochlorite and Calcium Hypochlorite in their 0.001- 0.1 N concentrations using Cl- ISE and Pt electrode:

10 ml of each sodium hypochlorite and calcium hypochlorite were transferred to the titration flask, 30 ml of distilled water were added in addition to 30 ml of 1M H2SO4. Both Cl- ISE and Pt electrode and calomel reference electrode were immersed in the solution and titrated with standardized iodide solution with stirring by magnetic stirrer until sudden change in potential. The titration was continued for several additions after equivalence point to get complete potential titration curve.

 

Standardization of double junction glass electrode:-

This electrode was standardized with pH4 buffer solution and pH =9.2 buffer solution in order to follow the pH change through titrations and find out its response efficiency.

 

Calibration of Cl- ISE:

The Cl- ISE was calibrated with standardized solution of Cl- in the range of 10-5–10-1 MWith stirring by magnetic stirrer. The calibration was done in aqueous solution of Cl- and in 0.1 N KNO3 solution. The calibration was repeated several times and the slope was found for each calibration and the mean was calculated.

 

Determination of hypochlorites in bleaching commercial solutions:

10g of each commercial bleaching solution of hypochlorite were accurately weighed and transferred to volumetric flask (250 ml) and completed to the mark with distilled water.10 ml of this solution were transferred into conical flask and diluted with distilled water (30 ml) and 30 ml of 1M H2SO4.Accurate volume of Iodide solution was added and the whole solution was back titrated with thiosulphate solution using starch as indicator. The titration was calculated and used to find out the percentage of hypochlorite in each commercial bleaching solution. The method was repeated by transferring 10 ml of bleaching solution to a beaker, diluted with 30 ml of distilled water and 30 ml of 1M H2SO4. The solution was titrated with standardized iodide solution using Cl- ISE and Pt electrode with calomel reference electrode until complete S curves are obtained and the percentage of ClO- was calculated.

 

Potential Selectivity Coefficient Measurements, KCl-, I- pot (17, 18).

Mixed solution method was applied to find out the effect of added I- solution on the response of Cl-ISE. The concentration of I- was kept constant and a series of Cl- solution was added (10 -5- 10-1M). The method was carried out with iodide concentrations of 10-3, 10-4 and 10-5 M respectively. The potential was plotted against log [Cl-] and the potential selectivity coefficient, KCl-, I-pot was calculated.

 

RESULTS AND DISCUSSION:

Calibration of Cl- ISE:

The Cl- ISE gave linear response range for (10-5- 10-1M) of chloride solutions, with a slope of -58.73±0.68 mV/ decade and R2 = 0.9991. The response was good and response time lasted less than 6seconds as shown in (fig.1A). The Cl- ISE was calibrated also for (10-5- 10-1 M)Cl- in 0.1 M KNO3, The response was more efficient with slope of -54.09±0.73 mV/ decade and R2 = 0.9978. The electrode response was rapid (lasted less than 3 sec) andmore stable than in the aqueous solution (Fig. 1B).

 

Potential selectivity coefficient of Cl- ISE(17, 18) :

Mixture solution method was applied to calculate the potential selectivity factor of Cl- ISE toward Cl- in presence of I-(Fig.2).The method shows interference in the range of 7.7 x 10-6- 9.4x 10-4(Table 2). Although these are low but they are significant which indicate to some extents the interferences of I- ions. However, The reaction of I- with OCl- occurs promptly and the released Cl- was responded at once by Cl-ISE.

 

(Fig.1B) Fig.1(A)

Fig (1) Calibration curves of Cl- ISE in the range of (10-5- 10-1 M) Cl- in aqueous solution (A) and in 0.1 M KNO3 solution (B).

 

Fig.2 : Titration curves of Cl- ISE toward Cl- in the presence of I-.

 

Table (2) : Values of the potential selectivity factors of Cl- ISE.

Concentration of I-

K Cl-, I- pot

10-Mar

9.4 x 10-4

10-Apr

8.8 x 10-5

10-May

7.7 x 10-6

 

Potential titration curves of sodium and calcium hypochlorites were obtained in concentration range of (10-3 – 10-1 M) using Cl- ISE and Pt electrode against calomel reference electrode.

 

Figs.3A and 3B showed the titration curves of sodium and calcium hypochlorites with iodide solution in acidic medium with different concentrations. The titrations showed clear sudden changes at equivalence points and S forms of the curves, which were supported by first and second derivatives (Figs. 4A and 4B).

 

 

 

Fig. 3A: Titration curves of sodium hypochlorite with iodide solution in acidic medium in different concentrations using Cl- ISE Vs Calomel reference electrode.

 

 

Fig. 3B:Titration curves of calcium hypochlorite with iodide solution in an acidic medium in different concentrations using Ptelectrode Vs Calomel reference electrode.

 

 

Fig.4A: First derivative to titration curve of sodium hypochlorite with I- solution using Cl- ISE Vs Calomel Referenceelectrode.

 

 

Fig. 4B : Second derivative of titration curve of sodium hypochlorite solutions with I- solution using Cl- ISE Vs Calomel reference electrode.

 

Fig. 5A: Titration curve of Health Company solutions with I- solutionin an acidic medium using Pt electrode VS Calomel reference electrode.

 

Fig. 5B: First and Second derivative of titration curve of Health Company solutions with I- solution using Pt electrode VS Calomel reference electrode.

 

Table (3):Potential titration results of sodium hypochlorite and calcium hypochlorite with iodide solution in acidic media with different concentrations.

No.

components

The Electrode

Added quantity (ppm)

Recovery (ppm)

Error

 

 

 

 

 

Percentage %

 

 

 

772

760

-2.14

1

NaClO.5H2O

Pt

686

671

-2.19

 

 

 

2

1.95

-2.5

 

 

 

944

957

1.36

 

 

Cl-

772

782

1.3

 

 

 

429

445

3.73

 

 

 

3432

3321

-3.27

2

Ca(OCl)2

Pt

343

330

-3.79

 

 

 

2.14

2.07

-3.27

 

 

 

4289

4421

3.08

 

 

Cl-

3432

3554

3.55

 

 

 

429

442

3.03

 

Table (4): Potentiometric titration results of hypochlorite with iodide solution using chloride ions selective electrode compared with platinum electrode.

Name of company

Date of manufacture

Date of Expire

Trade percentage on bottle

Found percentage Pt E

Found percentage

 

 

 

 

 

Cl- E

Oroplus

Mar-17

Mar-22

5%

4.64± 0.89

5.18%±0.26

Fas

Jul-18

Jun-19

6%

5.01±0.52

6.44±0.89

Lama'a

Aug-18

Aug-21

2%

2.51±0.52

3.04±0.26

Health

Jul-18

Jul-19

5-7%

4.65±0.26

6.08±0.52

Shoof

Jun-18

Jun-19

5%

4.11±0.26

5.34±0.45

Alwazir

Jan-18

Jan-23

4-6%

3.22

4.11±0.26

Peros

Sep-16

Sep-21

15%

2.36

3.55±0.26

Garden's Roses

Jul-17

Jul-20

12%

0.11

0.11

 

 

In order to find out the efficiency of both electrodes toward sodium hypochlorite and calcium hypochlorite, the added quantity and its recovery were calculated in addition to errors percentages. Table (3) shows titration results of these compounds with iodide solution in an acidic medium.

 

Inspection of table (3), it was found that the error percentages were from -2.14 to +3.55 which were attributed to practical errors in addition to iodide interference in Cl- ISE responses which gave positive errors. The results also clarified the high efficiency of both electrodes for determination of both sodium and calcium hupochlorides in their individual solutions. The molecular formula of ClO- (51.5) was used in the calculations of mass in liter of solution as ppm since both NaOCl and Ca(OCl)2 liberate hypochlorite in their solutions.

 

OCl-+ 2I-+ 2H+                               I2  +   Cl-  +  H2O

 

Determination of Hypochlorites in Commercial Bleaching Solutions :-

Eight bottled samples of commercial bleaching hypochlorites were bought from the markets under numerous trade names (Table 4). 10g of each bleaching bottle were accurately weighed and transferred quantitatively to volumetric flask (250 ml) and diluted to the mark with distilled water.10 ml of each diluted solution were transferred into a beaker, diluted with 30 ml of distilled water and 30 ml of 1M H2SO4.The solution was titrated with standardized iodide solution using Cl- ISE and Pt electrode with calomel reference electrode until complete S curves are obtained(fig. 5A).Equivalence points were marked and obtained from these curves and assisted or supported by first and second derivatives (Fig 5B).

 

The percentages obtained with Cl- ISE were calculated and compared with those obtained by platinum electrode (Table 4). The liberated iodine was titrated with standardized thiosulphate solution for comparison. Looking through table (4), it was found that various concentrations (percentages) are obtained. High percentages of hypochlorites contents were found with Oroplus, Fas, Health, and Shoof samples (ranged 4.11- 6.44 %) while lower percentages were obtained in bleaching solutions of Lama'a, Alwazeir, Perous and Gardens Roses (ranged 0.11- 4.11 %).The low values with both electrodes were attributed to the wasting of hypochlorite during long storing, the effect of high temp, through transferring, dilution and magnetic stirring of the samples under titration (19, 20).

 

The percentages of Gardens Roses samples were very traces (0.11%) in comparison with trade percentage labelled on the bottle (12%). The long period of storing between manufacture date and expire date was the main reason of this very low percentage determined by both electrodes, especially at summer season without cooling(12). House hold bleach sold for use in laundering clothes of wasting and decomposition is a 3-8% solution of sodium hypochlorite at the time of manufacture. Strength varies from one formulation to another and gradually decreases with long storage. Percentages of hypochlorites determined by Cl-ISE were relatively larger than those obtained by platinum electrode. Platinum electrode responds to Oxidation – Reduction potentials and there is no effects of by –product NaCl or iodide on its response. On other hand, Cl- ISE responds to Cl- produced by reduction of OCl-, little NaCl by –product in the manufacture of hypochlorite and iodide interferent added to hypochlorite solution during titration process. However, the difference is not so high but the percentages of hypochlorite in these samples are within the range 3-8% solutions of sodium hypochlorite during the period of storage (5).

 

In this research it was found that using 9 M H2SO4with the hypochlorites solution renders the reactivity of hypochlorite very high which spoiled the membrane of one Cl- ISE. Therefore, the concentration was lowered to 1M H2SO4.

 

CONCLUCTION:

1-       It was found in this research the high efficiency of Cl- ISE and Pt electrode in determination of hypochlorite in sodium hypochlorite and calcium hypochlorite.

2-       Cl- ISE and Pt electrode were successfully applied in determination of hypochlorites in commercial bleaching solutions.

3-       Error percentages were negative with Pt electrode and positive with Cl- ISE. These errors were attributed to practical errors and the interference of iodide ions.

 

ACKNOWLEDGMENT:

1-       The investigators would like to thank Medical Laboratory Techniques Department and AL-Maareff College University for approving and supporting this research.

2-       Dr. Khalid AL-Rawi, Mr. Ahmed Subhi, Mr Marwan A. Hassen in Chem. Dept, College of Science, University of Anbar, And Mr Adnan Fayadh in Big Ramadi water project, are highly acknowledged for their help, assistance and donating us of some necessary instruments and items in the practical side of the research.

 

CONFLAICT OF INTERESTS:

There are no conflict of interest.

 

ETHICS AND CONSENT:

Taken from Al-Maarif University College.

 

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Received on 09.04.2019         Modified on 17.06.2019

Accepted on 18.06.2019         © RJPT All right reserved

Research J. Pharm. and Tech. 2019; 12(11):5485-5491.

DOI: 10.5958/0974-360X.2019.00952.1